The invention is directed to a method and to an arrangement for positioning a magnetic head to various tracks of a storage medium of a magnetic layer storage.
In magnetic recording and playback, it is standard both given magnetic disc storages as well as magnetic tape storages to employ a magnetic head system that can be set to various tracks of the disc-shaped or tape-shaped storage medium. A number of tracks on the recording medium can thus be accessed with a relatively simple magnetic write/read head. The write/read head in magnetic disc storages is frequently composed of a single head system that can be positioned to a respective one of the many information tracks of the allocated storage disc with the assistance of a linear or rotary positioner.
By contrast, a greater number of designs of the magnetic head systems are known for magnetic tape storages. These extend from a simple magnetic head having only one gap, up to complex magnetic head systems having a plurality of parallel recording channels, i.e. multi-track heads. Different operating modes, moreover, are standard in magnetic tape devices. Thus, it is notoriously known to again immediately read information just recorded in order to be able to immediately correct recording errors as warranted. In this case, a write head and a read head arranged immediately following it in a tape conveying direction are required since the functions "record" and "read" must simultaneously sequence. It is also known to execute the two functions of "writing" and/or "reading" as well in both conveying directions of the magnetic tape. Without this enumeration being necessarily complete, it results therefrom that a number of different magnetic head systems are utilized in magnetic tape storages, depending on application and design.
All of these possible embodiments of magnetic layer storages thus share a number of fundamental boundary conditions. The development tendency in all magnetic layer storages is still in the direction toward increasing the storage capacity, given simultaneously improved dependability, i.e. a reduced error rate when writing and/or reading. The storage capacity in the track direction can be increased by increasing the flux changes per length unit. The increased bit density, however, leads to a reduced read signal amplitude, to signal interferences due to shifts of peak values, and thus to a higher risk that a recording pulse will be suppressed. Even with improved storage media and storage heads, therefore, the bit density cannot be arbitrarily increased. The other possibility of enhancing the storage capacity is to increase the track density. However, it thus becomes more and more difficult to read the information tracks that become narrower and narrower or, in more general terms, to exactly position the magnetic head to a selected information track.
In view of this trend, the significance of tolerances in the mechanical structure of a magnetic head system itself, as well as the mounting to a magnetic head carrier, increases, as does the overall positioning means which positions the magnetic head system with respect to the information tracks of the storage medium. This is again valid in the same way both for different magnetic head systems as well as for different positioning devices, even though the individual tolerances that can be designed in with reasonable expense may differ from case to case.
U.S. Pat. No. 4,679,104, incorporated herein by reference, already discloses that the effect of these tolerances can definitely differ, even given individual units of magnetic head systems of the same type, and that it is therefore necessary to individually acquire these effects in order to be able to precisely position. The above publication discloses a method and an arrangement for positioning a magnetic head to various tracks of a magnetic tape, whereby control signals for a motor-driven displacement of the positioner unit are generated by comparing respective actual position values of the magnetic head to rated position values that are allocated to the various tracks of the magnetic tape. These control signals are generated for a motor controller of the positioner means in the normal operation of the magnetic tape storage by use of stored position values. These position values are identified during a measuring event wherein the magnetic head system is moved from a defined reference position and is positioned to the middle of at least one track, and wherein this position is allocated to a defined, measured position value. According to the known, technical teaching, these position values can be composed of nominal values that are valid for a plurality of magnetic tape recording means of the same type, and are composed of individual correction values that are individually calculated for every magnetic tape recorder means. The basic idea on which this known solution is based is to input defined, respectively individually measured values into the controller of each and every individual magnetic tape recorder means, on the basis whereof the means is in the position to take individual tolerances in the respective magnetic tape recorder means into consideration in every positioning event, i.e. to compensate them.
This known method definitely satisfies demands, given today's commercially available magnetic tape recorder cassette devices having approximately up to 30 parallel information tracks on the magnetic tape. The problem, however, is that the correction values measured therewith are themselves still relatively imprecise because the measurement for calibrating the individual tape drive is itself still affected by errors. This is critical in storage devices having an interchangeable storage medium, for example magnetic tape recorder cassette devices. According to the known method, the individual tolerances of the positioner means vis-a-vis such a magnetic tape and cassette unit is acquired in a commercially available design. During normal operation, however, the cassettes described in this fashion can be introduced into different tape drives. If, given retention of the known calibration method, one would like to further increase the storage capacity in such devices, one would nonetheless have to keep these tolerances low--despite the desired tolerance compensation--with an expense that could not be justified for cost reasons in order to guarantee full compatibility.